Currently, positive photoresists are widely used for formation of circuit patterns of electronic devices or the like. As positive photoresist compositions which can be used for these applications, combinations of alkali-soluble novolac resins and quinone diazide compounds as sensitizers have often been used.
In this kind of composition, there is utilized a reaction in which a quinone diazide group is photolyzed by irradiation with ultraviolet rays to form indenecarboxylic acid via ketene. However, in the resist formed by using the quinone diazide compound, a resolution is insufficient sometimes in a case where it is necessary to form a very fine pattern.
On the other hand, Japanese Patent Application Laid-open No. 295064/1994 discloses a photosensitive composition comprising a carboxyl group-containing polymer, a compound containing two or more vinyl ether groups in one molecule, and a compound which generates an acid when irradiated with activation energy rays. When a film formed from this composition is heated (primary heating), a polycarboxylic acid resin is cross-linked by an addition reaction between a carboxyl group and a vinyl ether group, so that the film becomes insoluble in a solvent or an aqueous alkaline solution. Furthermore, when the film is further heated (secondary heating) after the irradiation with the activation energy rays, the cross-linked structure is cleaved owing to a catalytic action of the acid generated by the activation energy rays irradiation, so that the irradiated portion becomes soluble in the solvent or the aqueous alkaline solution again. Then, the irradiated portion is removed by development to form a resist pattern.
The above-described method, in which the circuit pattern is formed by heating the photosensitive composition comprising the polycarboxylic acid resin, the polyfunctional vinyl ether compound and the compound which generates the acid when irradiated with the activation energy rays, can basically satisfy a request for the formation of the very fine circuit pattern in recent years. However, in order to cleave the cross-linked structure of the irradiated portion after the activation energy rays irradiation, the heating process is essential, and it is required that the heating process is carried out at 60 to 150° C. for 10 to 60 minutes. The addition of such a heating process (secondary heating) decreases a production speed in a pattern formation process and further may cause another problem such as deformation of a substrate owing to the heating at high temperature. Furthermore, since the acid component generated by the light irradiation diffuses in the resist film owing to the secondary heating, there is also another problem that the resist film having the excellent resolution cannot be obtained.